The disclosure of Japanese Patent Application No. 2001-349130 filed on Nov. 14, 2001 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to a power source unit of a vehicle and the like. More particularly, the invention relates to a power source unit in which a plurality of chargeable/dischargeable batteries are provided.
2. Description of Related Art
As a power source unit having a plurality of chargeable/dischargeable batteries, there is a known power source unit, as disclosed in Japanese Patent Application Laid-Open No. 2000-50402, which is mounted in a hybrid vehicle having a combination of an internal combustion engine and a motor. More specifically, as shown in FIG. 5, a power source unit including a high voltage main battery 101 and a low voltage accessory battery 102 causes a motor generator (M/G) 104 to generate electric power by driving an engine 103. The power source unit then charges the main battery 101 via an inverter 105 such that the motor generator 104 is driven by electric power of the main battery 101. A DC-DC converter 106 is provided between the main battery 101 and the accessory battery 102 so as to transfer power therebetween.
The aforementioned power source unit requires the DC-DC converter 106 for the purpose of charging and discharging the accessory battery 102. This may result in the cost increase. More specifically, the DC-DC converter requires a converter including an AC/DC converting circuit at a high voltage side, an AC/DC converting circuit at a low voltage side, a transformer and the like, and a step-up switching circuit required for charging the main battery 101 by the accessory battery 104. The resultant configuration of the DC-DC converter 106, thus, becomes complicated, increasing the cost.
It is an object of the invention to provide a power source unit that allows charging and discharging of a plurality of batteries at low costs.
According to an exemplary embodiment of the invention, a power source unit includes an inverter connected to a power transfer device, a first battery that can be charged and discharged through the inverter, and a second battery that can be charged and discharged through the inverter. A power voltage of the second battery is lower than that of the first battery. The power source unit further includes a power conversion device connected to the inverter, providing a transforming function, and a switching device provided between the power conversion device and the first and second batteries. The switching device switches a connection between the power conversion device and the first battery, and the power conversion device and the second battery. The inverter is connected to the first and the second batteries through the power conversion device. The power conversion device includes a transformer, a first bridge circuit connected to a primary side of the transformer, and a second bridge circuit connected to a secondary side of the transformer.
Further, the switching device includes a switching circuit that switches the connection between the power conversion device and the first battery, and the power conversion device and the second battery.
Still further, the switching device includes a coil connected between the first battery and the second battery through the switching circuit. The power transfer device includes a motor generator, and the inverter allows rectification of an alternating output of the motor generator so as to supply an alternating current to the motor generator.
The power source unit is preferably provided in a hybrid vehicle driven by the power transfer device for a running operation.
According to the aforementioned embodiment that allows switching of the connection between the power converter and the first battery, and the power converter and the second battery, electric power generated by the power transfer unit can be selectively supplied to the first battery or the second battery for charging. It is also possible to selectively supply electric power stored in the first battery or the second battery to the power transfer unit. The exemplary embodiment of the invention does not require a step-up circuit such as the DC-DC converter in addition to the converter. As a result, the first battery and the second battery can be charged/discharged without the converter, thus reducing the cost for parts.
Moreover, as the inverter is connected to the first battery and the second battery through the converter, it is possible to bring an input/output voltage on the battery side of the inverter into a high voltage state. This feature makes it possible to use components of low electric current type for forming the inverter, thus reducing the size and cost of the inverter. This feature becomes especially effective when one of the first battery and the second battery at the high voltage side is of 30 to 42 V type.
Furthermore, the coil connected between the first battery and the second battery via the switching circuit may cause the power converter and the switching unit to function as the step-up choppers so as to allow power transfer between the first and the second batteries.